This invention relates to an improved spiral separator.
Spiral separators are used extensively for the wet gravity separation of solids according to their specific gravities, for example in separating various kinds of mineral sands from silica sand, or in cleaning crushed coal by the removal of ash and other impurities.
A spiral separator consists usually of a vertical column about which there are supported a number, commonly two, of helical troughs or sluices, generally known as "spirals". The spirals are of constant or uniform pitch, corresponding parts of the spirals of a two-start spiral separator being diametrically opposed at the same level. A "pulp" or slurry of the materials to be separated and water, is fed at a predetermined rate into the upper ends of the spirals, and as the fluid mixture passes down through them it tends to form bands of strata of minerals of different specific gravities. These strata are separated at intervals by adjustable splitters, the mineral fractions which are required to be recovered, and which are thus separated, being carried away through take-off openings, wash water being introduced at intervals to the inside parts of the spirals to correct the pulp density and prevent "sand-barring" or the formation of stationary deposits of the material of lesser specific gravity on the bottom of the spirals.
A separator of this type is of fairly complex character, with its numerous adjustable splitters, which may require re-adjustment from time to time, and with the hoses connected to and leading down from the take-offs, and the hoses feeding wash water at intervals to each spiral, any of which hoses may become blocked by fibrous particles and require to be cleared. The separator, then, is expensive to manufacture, and requires fairly constant attention at a number of points to achieve acceptable results.
Normally, spiral separators of this type are used to separate the required materials by a number of successive and interrelated treatments. Thus, in the first pass, the material is divided into a heavy fraction or concentrate and a light fraction or tailings; the heavy fraction is re-treated to produce a concentrate and a tailing, which is combined for re-treatment with a heavier fraction split from the tailing of the first pass, and so on. At each stage, the volume of tailing which is thrown, or discarded, as containing only an insignificant amount of the mineral to be recovered, is not substantial. The repeated re-treatment of much of the pulp is, of course, slow and expensive.
The present invention has been devised with the general object of providing a spiral separator which, as well as being simple and economical to manufacture and operate, may be used to produce a rich concentrate and throw a very substantial final tailing on a single pass of material through the apparatus, a middling cut being taken for re-treatment.